Mustard algae shock in vinyl pool - advice and bleaching risk

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Nidstang

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Nov 24, 2018
5
Perth, Western Australia
Hi all. I have noticed what appears to be mustard algae clinging to the shaded wall (I let the chlorine level run low so it's my fault). It was yellow in colour and easily removed by brushing. The water is still clear. I'm following the SLAM procedure using liquid chlorine.

1. Is there any risk of fading my blue vinyl liner at mustard algae shock level, which in my case is 39? I found one relevant thread which had me concerned:

So it looks like I bleached my Vinyl Liner during my Mustard Algae SLAM

I had to SLAM my one year old pool after getting mustard algae. When I started the SLAM, my CYA was at 65 so I brought my FC levels up to 26 until I passed the CC and overnight test. Then I raised my FC to 37 for 24 hours for mustard algae. I went out of town for 4 days after the mustard...
www.troublefreepool.com www.troublefreepool.com
This thread reassures the user that SLAM levels are safe for vinyl liners, but no mention of mustard algae shock levels:

Risk of bleaching liner with SLAM?

FC 7.2, pH 7.6-7.7, TA 90, CYA 50 (CYA from pool store electronic test) I have an algae problem and need to SLAM my pool. Based on the chart Chlorine / CYA Chart - Trouble Free Pool and my CYA level (which I find impossible to test myself as I ALWAYS see the little black dot!), I need to bring...
www.troublefreepool.com www.troublefreepool.com

2. Is the 24 hour mustard algae shock absolutely necessary or can I maintain SLAM level and monitor over time?

3. I thought CC was an indicator that chlorine was being consumed, but my CC is always below 0.5. Is this normal?

4. This might have contributed. My SWG max setting (i.e. the number of LEDs that light up) changes. Sometimes it only winds up to 70%, then next I look it is lit up at 100%. It is no longer consistent. What could cause this?

5. Do I need to run the pump overnight? What about during overnight chlorine tests?

Here are my current levels, thanks!
pH 7.7 (never changes, although I did just add acid aiming for 7.2. Generally it always sits at 7.7 and I can't maintain lower than this. I think because I regularly top up with tap water because I don't have a cover and evap is high)
FC 23 (will increase to 28 tomorrow or as recommended here)
CC <0.5
CYA 70
TA 125 (never changes)
CH 250 (never changes)
Salt 4900
 
I'm answering each question in your post individually- please expand quote to see:

Nidstang said:
1. Is there any risk of fading my blue vinyl liner at mustard algae shock level, which in my case is 39? I found one relevant thread which had me concerned:
Just to reiterate the directions for Mustard Algae- you're only bringing the FC up to that higher level for the *last 24 hours*, not using that as your FC level throughout the SLAM process. I will say that organic blue dyes are the most vulnerable dye color on liners, but I've never read anyone say that the mustard algae day damaged the liner.

2. Is the 24 hour mustard algae shock absolutely necessary or can I maintain SLAM level and monitor over time?
Its your call if you're going to perform the SLAM process for mustard algae as directed. You'll be the one re-doing it if it isn't enough.

3. I thought CC was an indicator that chlorine was being consumed, but my CC is always below 0.5. Is this normal?
Yeah, oddly enough not all algae causes CCs to rise....yet it *is* algae. And some perfectly fine pools always have 0.5ppm of CC. Its more a matter of knowing your pool.

4. This might have contributed. My SWG max setting (i.e. the number of LEDs that light up) changes. Sometimes it only winds up to 70%, then next I look it is lit up at 100%. It is no longer consistent. What could cause this?
SWGs don't work around the clock, they cycle on and off. Without knowing more, and assuming yours does maintain your desired FC level normally I wouldn't worry about it. You can also check your salt level to make sure its meeting the SWG's required amount.

5. Do I need to run the pump overnight? What about during overnight chlorine tests?
During a SLAM process, the more often you can perform the tests and re-dose as necessary, the faster it usually goes. A least 3x a day will do it too. Yes, you want your pump to continue to mix and circulate the chlorinated water. Don't forget to brush daily!

Here are my current levels, thanks!
pH 7.7 (never changes, although I did just add acid aiming for 7.2. Generally it always sits at 7.7 and I can't maintain lower than this. I think because I regularly top up with tap water because I don't have a cover and evap is high)
FC 23 (will increase to 28 tomorrow or as recommended here)
CC <0.5
CYA 70
TA 125 (never changes)
CH 250 (never changes)
Salt 4900
Click to expand...

Please don't try to adjust your pH when your FC is over 10. That higher FC level invalidates the pH test, so you don't want to overshoot something which *can* damage your vinyl liner. Just wait till your FC is <10 and check it again. Evaporation has more affect on CH and salt than pH.

SWG pools *like* 7.7-7.8 for some reason.... just go with the flow. Its still within normal limits.

Your SLAM process FC level is 28, as you know, but once you feel you are done you will then raise the FC to 41 for the last 24 hours.

Maddie :flower:
 
Thanks Maddie. I just did the overnight test and FC dropped 0.5.

Is there a way to lower the chlorine level after the 24 hr shock period or do you let it naturally drop? Weather forecast here is cloudy for the next four days and raining so should I wait to do the shock before a sunny day? I don't want to run the FC 41 level for too long and I don't have a feel for how much it will naturally drop through the day, but I'm assuming it's from sunlight.

If I hold off for a few days, what is the minimum safe holding FC level? Thanks :)
 
Normally folks just let the FC lower naturally. You don't want it lowered if you're going to hold off on the mustard algae day- just keep it at the normal SLAM process level until that final day.

HIgh chlorine levels actually degrade faster than lower levels. Since the CYA is all saturated, that excess chlorine is just food for the sun-gods.

Maddie :flower:
 
If you feel you *must* lower the FC after a day, you can buy Thiosulphate from a pool store. You risk over-doing it though, and don't want to use more then find your FC at zero.

Calculator or instructions for sodium thiosulfate?

Hello! I wanted to know if there is a calculator or instruction sheet y'all recommend for how much sodium thiosulfate to add in case my free chlorine gets out of whack again from over-zealous shocking. (it was as high as 65 before dumping in about 24 oz yesterday, dropped like a rock) I've...
www.troublefreepool.com www.troublefreepool.com
 
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